1. Technical Field
This disclosure relates to an image processor that carries out image processing on image data that is output in an image forming apparatus.
2. Description of the Related Art
Recently, it is widely known that in an image forming apparatus such as a multi function peripheral (MFP) or a printer etc., a toner scatters during fixing due to asperities that occur in an image portion, or due to a level difference that occurs in a boundary of the image portion and a non-image portion. Due to this, image quality significantly deteriorates.
Further, to improve the image quality, some of the image forming apparatuses use a transparent toner or a white toner apart from normal color toners of cyan (C), magenta (M), yellow (Y), and black (K) colors.
In a method disclosed in Japanese Patent Application Laid-open No. H6-175461, four color developing units, which develop a corresponding image with a corresponding color toner, and one transparent developing unit, which develops a corresponding image with a transparent toner, are arranged in a transfer unit. Electrostatic latent images on photosensitive drums are developed with color toners, and a non-image portion on the photosensitive drums is developed with the transparent toner. This approach makes it possible to match the heights of the toner layer in the image area and the non-image area and to eliminate the asperities of the image surface. Further, Japanese Patent Application Laid-open No. 2005-37431 teaches to develop the non-image area with a transparent toner to equalize an abrasion rate of the photosensitive drums.
Japanese Patent Application Laid-open No. H7-5738 discloses to overlap a transparent toner on an asperity portion of a multicolor image and then fix the image to a transfer sheet. With this approach, it is possible to round off the asperities of the multicolor image arising due to overlapping of the color toners, as well as eliminate occurrence of an incompletely melted toner portion during fixing.
In a method disclosed in Japanese Patent Application Laid-open No. 2001-341352, a white toner is coated on shaggy jags that occur in a slanting edge portion, the resulting image is printed, edges of shaggy corners are eliminated, and shaggy portions are smoothened to get a smoothing effect, thus recreating a lustrous image.
However, in the methods disclosed in Japanese Patent Application Laid-open No. H6-175461 and Japanese Patent Application Laid-open No. 2005-37431, because the transparent toner is developed in the entire non-image portion, a consumption of the transparent toner increases, thus increasing a running cost.
Further, in the method disclosed in Japanese Patent Application Laid-open No. H7-5738, an asperity difference between a developing portion where the multicolor image and the transparent toner are developed and a non-developing portion increases. Due to this, the toner scatters during fixing in such a boundary portion and the image quality deteriorates. In an electrophotograph, a light amount and a pulse width of a laser are changed to carry out multiple grayscale control inside a single dot. Carrying out the multiple grayscale control inside the single dot, in other words, developing the image using a faint light exposure results in occurrence of dots in which the toner is not sufficiently accumulated. Thus, the asperities of the toner layers are not eliminated in the method that is disclosed earlier.
Further, in the method disclosed in Japanese Patent Application Laid-open No. 2001-341352, because the white toner is not coated adjacent to vertical lines and horizontal lines, if an image such as a table is output, the toner scatters during fixing and deterioration of the image quality cannot be curbed.
Combining and using the technologies that are disclosed in Japanese Patent Application Laid-open No. H7-5738 and Japanese Patent Application Laid-open No. 2001-341352 enables to curb scattering of the toner during fixing due to the asperities that occur in the image portion and due to the level difference that occurs in the boundary of the image portion and the non-image portion. However, because processes need to be carried out individually, efficiency is reduced.